Liquid metal operated vapor generator



May 31, 1966 N. D. ROMANOS 3,253,648

'l INVENTOR:

MCHOLAS D. ROMANOS ,/BY WM; @M1

f N' ATTORNEY May 31, 1966 N. D. RoMANos LIQUID METAL OPERATED VAPOR GENERATOR 4 Sheets-Sheet 2 Filed June 18, 1963 wm mw NS 5 May 31, 1966 N. D. ROMANOS LIQUID METAL OPERATED VAPOR GENERATOR 4 Sheets-Sheet 5 Filed June 1S, 1963 INVENTOR ATTORNEY NxcHoLAs D. RoM'ANos mm mw S mw Qm May 31, 1966 N. D. RoMANos LIQUID METAL OPERATED VAPOR GENERATOR 4 Sheets-Sheet 4 Filed June 18, 1963 INVENTOR. NiCHOLAS D. ROMANOS BY WM? C' ATTORNEY United States Patent O M 3,253,648 LlQUlD METAL OPERATED VAPOR GENERATOR Nicholas D. Romanos, Chattanooga, Tenn., assigner to Combustion Engineering, Inc., Windsor, Conn., a corporation of Delaware Filed .lune 18, 1963, Ser. No. 283,784 Claims. (El. 165-81) The present invention is a continuation-in-part of U.S. patent application Serial No. 255,124, tiled January 30, 1963 and entitled Liquid Metal Operated Vapor Generator, and now abandoned.

This invention relates to heat exchangers for effecting the safe transfer of heat between two actively reactive liuids. More particularly, the invention relates to a compact vapor generator constructed of a plurality of structurally similar heat exchange elements capable of safely transforming water into steam through the use of liquid sodium as a heating liuid and capable of withstanding thermal expansion without incurring undue strain.

Liquid metal-cooled nuclear reactors have been ernployed as highly efficient sources of heat for the generation of vapor utilized by conventional steam powered equipment such as turbines and the like. However due to the violent nature of the reaction between liquid metals, such as sodium, and water, it is necessary to insure that the two fluids are kept separate. To accomplish this, such vapor generators normally employ an intermediate, non-reactive fluid in heat exchange relation between the two operating fluids whereby heat is transferred first from the' liquid metal to the intermediate iiuid and then from the intermediate fluid to the water to effect the transformation of the latter into steam. This arrangement is both costly and cumbersome in that it requires the employment of an additional iiuid circuit with its concomitant equipment, such as tanks, liuid lines, and the like. Moreover, such units are less efcient to their operation because of the heat loss experienced in transferring heat from a first operating fluid to an intermediate uid and then to the final operating fluid.

exchange elements are so designed as to form continuous fluid circuits free from welds in the zone where the watercontaining tubes are in Contact with sodium. Therefore should leaks develop in the welds, any leakage, either of sodium or of water, would result in the leaking uid being passed into space rather than into contact with the other fluid.

Each of the heat exchange elements are formed identically so as to embodyI the modular design concept. The vapor generator is designed to employ elements having identical shape and dimensions and a desired increase or decrease of generator capacity for subsequent units does not require the redesign of each element but instead, the construction of subsequent units can be arrived at merely by calculating `the number of heat exchange elements necessary to arrive at the desired calculated capacity.

Additionally, as a result of the utilization of a multiplicity of small diameter shells to contain the pressurized fluids the wall thicknesses of such shells are considerably reduced to thereby minimize the problem of thermal stress inherent in heavy walled pressure vessels.

Moreover, each of the heat exchange elements is so formed that expansion and contraction thereof caused by changes in metal temperature will not result in the overstressing of any of the parts or of their communication with other pressure parts employed in the generator.

3,253,543 Patented May 3l, 1966 This feature is accomplished in part by the fact that the two legs comprising each of the V-shaped elements are formed of a different length, the hot leg being shorter than the cold leg by an amount proportionate to the average metal temperature of each leg so that, during steady state operation, the two legs undergo approximately the same amount of thermal expansion and thus avoid undue strain in the tubes containing the two iiuids as well as in the tube terminals connecting the elements to ow headers. The feature is further accomplished by the fact that means are provided to positively effect uniform expansion of the higher temperature portion of the heat exchange elements in such a manner that the connectors uniting the heat exchange elements to the upper manifold headers are not unduly stressed during operation of the vapor generator,

It is accordingly an object of the present invention to provide a vapor generator capable of safely transferring heat between reactive liquids in an operatively eicient manner.

Another object of the invention is to provide a modular type of vapor generator employing heat exchange elements so constructed as to permit the design of subsequent units having diverse capacities by merely increasing or reducing the number of elements employed therein.

Yet another object of the invention is to provide a vapor generator employing heat exchange elements so designed as to permit thermal expansion and contraction of the pressure parts without causing severe stressing thereof. I

An additional object of the invention is to provide a liquid-metal operated vapor generator which is compact in form and eiiicient in operation wherein the hazards of employing highly reactive operating iiuids are minirnized.

Various other objects and advantages will appear from the following description of one embodiment of the invention, and the novel features will be particularly pointed out hereinafter in connection with the appended claims.

The invention is described 4with reference to the ticcompanying drawings wherein:

FIG. l is an isometric representation of a vapor genera` tor incorporating the inventive design wherein a number of the heat exchange elements and the greater portion of the casing and support structure have been removed for the sake of clarity;

FIG. 2 is a side elevation of the vapor generator design shown in FiG. l;

FIG. 3 is a rear elevation of the vapor generator design shown in FIG. l;

FIG. 4 is an illustration of one heat exchange element incorporated in the present vapor generator design;

FIG. 5 is a section taken along line 5 5 of FIG. 4;

FIG. 6 is a section taken along line 6 6 of FIG. 4;

FIG. 7 is a section taken along line 7 7 of FIG. 4;

FIG. 8 is an isometric representation of one end of a typical heat exchange element such as that shown in FiG. 4 wherein portions of the external surfaces have been removed in order to show the internal structure thereof;

FIG. 9 illustrates in detail the means for establishing a point of fixation for the sodium main inlet circulator and the vapor outlet circulator;

FIG. 10 is a partial section taken through line 10 10 of FIG. 2 illustrating the spacer structure employed in the instant vapor generator design; and

FIG. l1 illustrates in detail the force applicator ernployed in the instant vapor generator design.

In the illustrated embodiment of the invention, the vapor generator 10 comprises a plurality of heat exchange elements arranged for the transfer of heat from a liquid metal heating fluid to a vaporizable fluid to be heated in order to generate vapor capable of being employed in vapor operated apparatus. For the sake if illustration,

the fluids employed in the vapor generator will be Considered to be liquid sodium as the heating fluid and water as the vaporizable fluid or the uid to be heated, although it is to be understood that the invention is intended for use with any uids which Aare desirably maintained separate while transferring heat from one fluid to another.

As shown in FIG. l, the vapor generator 10 Vcomprises a plurality of vertically disposed, V-shaped heat exchange elments 12 arranged in closely nested, parallel rows so as to permit the use of a large number'of elements in a limited amount of space. All of the elements 12 are dimensionally and structurally identical, therefore the herein contained description will be confined to a single heat exchange element, a typical example of which is shown in FIGS. 4-8. The illustrated heat-exchange element 12 comprises an elongated cylinder shell 14 which is formed generally in the shape of a V having an upper leg 16, a lower leg 18 and a bend or apex 20. In constructing the shell 14 a pair of cylindrical tubes which form the legs 16 and 18 are arranged obliquely with respect to an imaginary horizontal line, the slope being such as will facilitate draining the element when it is assembled in the vapor generator. As best shown in FIG. 4, the legs 16 and 18, which are of unequal length for reasons to be hereinafter disclosed, are connected at the apex 20 by means of a union formed of U-shaped semi-elliptical shell halves 22 which form a bend, elliptical in section, when the assembly is completed. The elliptical shape of the bend 20 provides abundant clearance between the shell 14 and the tubes 38 extending through the shell so as to accommodate the lrelative expansion and contraction of each during operation of the vapor generator.

The ends of the shell14 are closed by means of closure lplates 24 which are attached to the shell by a fluid irnpervious weld 26. Adjacent each end of the shell 14 are located nozzles 28 and 30 which permit the ingress and egress of liquid sodium. Nozzle 28, located adjacent the upper end of the shell 14, is designated the inlet nozzle and is connected to a sodium inlet header 32 by means of tubular connector 34. Similarly, nozzle 30, designated the outlet nozzle and located adja-cent the lower end of the shell 14, is connected to a sodium outlet header 36 by means of a similar connector 34. Sodium inlet and outlet headers 32 and 36 are connected to a source of supply, such as the coolant portion of a nuclear reactor, by means of, sodium main linlet and outlet distributors 74 and 76 which serve to distribute the heating fluid to the heat exchange elements 12 through the headers.

Through the shell 14 pass a plurality of vaporizable fluid conducting, elongated tubes 38 which are enclosed by and co-extensive with the shell. These tubes 38, which number seven in the preferred embodiment, are positioned Within the shell 14 in spaced relation from the wall thereof and also spaced from each other in order to permit the free circulation of heating iluid about the surface of the tubes. The tubes 38 extend beyond the ends of shell 14,

their passage through 'the closure plates 24 being accommodated by means of apertures 40 contained therein. Welds 42 are applied around the outer surface of the tubes 38 to attach them to the closure plate 24 and provide a seal between the junction of the shell 14 and the tubes 38. Spaced from the ends of the shell 14 are fluid manifolds 44 and 46 which serve to unite the tube cluster in uid circulation. Mani-fold 44 is located at the upper end of the heat exchange element 12 and constitutes the vapor outlet manifold and manifold 46, located at the lower end of the element 12, is the liquid inlet manifold. The manifolds 44 and 46 are formed with a base 48 containing apertures 50 through which the ends of the tubes 38 are adapted to pass and a hemispherical head 52 attached to the base to form a chamber 54. Welds are applied to seal the ends of the tubes 38 to the base 48. The head 52 contains a central openi-ng 56 which permits communication of the chamber 54 with vaporizable uid inlet and outlet headers 58 and 60, communication therebetween being made by means of connectors 62. The vaporizable fluid inlet and outlet headers connect, in turn, with uid distributors, the former being the fluid inlet distributor 78 and the latter, the vapor outlet distributor 80.

To maintain the tubes 38 in spaced relation within the shell 14 mounting spacers 64 'are employed at longitudinally spaced points along the length of the heat exchange element 12. The spacers 64 are formed, as shown in FIG. 5, of a pair of peripheral strips 66 formed of bar stock and adapted to surround the cluster of tubes and a pair of median strips 68 which mutually encompass and engage the center tube 38. The ends of the strips 66 and 68 are joined at their ends to form a unitary member by means of welds 70. The' peripheral strips 66 are indented inwardly as shown in the figure to provide spaces 72 and 73 to permit the flow of uid through the shell 14. The mounting spacers 64 snugly maintain the tube cluster within the shell 14 but are free to float therein in order to permit the unencumbered relative expansion and contraction betweenl the tubes 38 and the shell 14.

The vapor generator assembly is enclosed by a pressure 'tig-ht casing 82 formed of blocks of insulation material system comprises a pair of centrally located longitudinal supports 88 from which a plurality of spaced lateral supports 90 extend. The ends of the lateral supports 90 are attached to vertical supports 92 and form a frame about casing 84. The vapor outlet circulator 80 is suspended from the central supports 88 by means of U-shaped brackets 94 which secure the distributor to the supports.'

The sodium main inlet distributor 74 is, in turn, suspended from the Vapor outlet distributor 80 by means of straps 96 which are positioned at spaced points along the length ofthe two distributors and which bind them together. The vaporizable fluid inlet distributor 78 is mounted at the base of the unit by means of saddles 98. Atop the intermediate saddles 100 is mounted, the sodium main inlet distributor '76. Straps 96 bind the two distributors, 76 and 7 8, together.

' vThe vapor outlet distributor 80 and the sodium main inlet distributor 74 are fixed with respect to the support system at a point intermediate their length to establish a point of zero longitudinal expansion or a point of xation designated as 102 in FIG. 2. The structure by which this point of fixation is established is best shown in FIG. 9 as being by means of a depending lug 104 which is weldedly attached to the bottom surface of one of lateral supports 90. Engaging members 106 are welded to the upper portion of the vapor outlet distributor 80 on both sides of the lug 104 in closely adjacent relation thereto so as to prevent any longitudinal movement of the distribf utor at this point, Another lug 108, similar to the lug 104 is attached to the lower surface of the v apor outlet distributor 80 in alignment with the aforementioned lug 104. This lug is adapted to engage engaging members 106 attached to the top surface of the sodium main inlet distributor 74 to similarly prevent longitudinal movement thereof at this point.

The support structure for the bundles of heat exchange elements i12 which form the heat transfer portion of the unit comprise laterally extending supports 110 which are suspended from the supports 90 by means of hanger rods 112. As shown in FIG. 2, the lowermost supports 110 in the rear portion of the assembly are suspended from intermediate supports 114 rather than from the lateral supports 90.

One of the several methods usable for spacing of the heat exchange elements 12 is shown in FIG. l0. It comprises the provision of sinuously shaped bearing spacers 116 which have one end weldedly attached to the supports 110 and which wind through the bundle as shown in the figure. The thickness of the spacers is equal to the width of the space between adjacent heat exchange elements such that all of the elements bear on the spacers thereby eliminating any clearance therebetween.

The operation of the vapor generator thus far disclosed is as follows. Vaporizable fluid in the form of water is admitted to the iuid inlet distributor 78 under pressure and is distributed throughout the unit through the inlet headers 5S from whence it is caused to flow through the tubes 38 in the heat exchange elements 12. At the same time heating liuid in the form of liquid sodium is admitted to the unit through the sodium main inlet distributor 74 from whence it is distributed to the heat exchange elements 12 by means of the inlet headers 32. The Water which ows through the tubes 38 Within each of the heat exchange elements -12 is therefore caused to come into heat transfer relation with the liquid sodium flowing downwardly through the shells 14, extracting heat therefrom to thus be transformed into vapor which emerges from the vaporizable iluid outlet manifolds 46 and thence from the vapor outlet distributor 80 while the sodium emerges from the sodium outlet distributor 76.

The present vapor generator is considered to be the once-through type in that vthe water in ilowing from the inlet end of the heat exchange elements 12 to the outlet end thereof extracts a suicient amount of heat from the liquid sodium to be transformed entirely into vapor or even to contain some amount of superheat. Because of the fact. that the generator is not of the circulation type wherein only a portion of the water is transformed into vapor, there is no need to provide vapor separating equipment, circulation pumps and the like to recirculate that portion of the duid which is not transformed into vapor through the generator.

Because the sodium main inlet distributor 7'4` and the vapor outlet distributor 80 are both located in the upper portion of the vapor generator 10, it can be seen that the upper portion of the generator, i.e. that portion above the imaginary plane formed by the bisectors of the apices 20, will be considerably hotter than the lower portion. This is so because both the heating medium and` the vaporizable iiuid experience their highest temperatures within the upper portion of the generator and since the components of the generator located in the upper portion thereof are subjected to higher temperatures than those located in the lower portion, they will be subjected to a greater amount of thermal expansion than the latter. In addition, because of the adverse eiect of temperature upon the strength characteristics of the structural materials employed, these components are considerably less capable of withstanding undue amounts of stress than are those located in cooler regions of the unit. Therefore means are provided to prevent subjecting the components to undue amounts of thermally induced stresses.

In the instant generator means are provided to insure that overstressing will not occur particularly in the connectors 34 which, due to their relative size, are the least capable of withstanding severe overstressing. This means includes first, a means for insuring that the amount of expansion occurring in the upper or hot leg 16 of each of the heat exchange elements 12 is the same as that which occurs in the cooler lower leg 18 such that the relative expansion between each will be the same thus alleviating some of the stress imparted to the connectors 34 which unite the elements 12 to the headers 32 and 36. Secondly, means are provided to insure that the upper or hot leg 16 of each of the heat exchange elements 12 is positively induced to expand with the other generator components and not be prevented from doing so by the friction forces 6 generated between the surfaces of the expanding shell 14 and heat exchange element spacers 116.

The first of the above-mentioned means comprises the formation of the legs 16 and 18 of the heat exchange elements 12 of different lengths, the upper leg 16 which is subjected to the higher metal temperatures being shorter in length than the lower leg 18 by an amount proportionate to the average metal temperature of each leg so that, during steady state operation of the generator the two legs will have approximately the same amount of thermal expansion to avoid the development of unequal strain in thel connectors 34 and 62 joining the elements 12 to the headers 32, 36, 58 and 60.

The second means contemplates the provision of a device adapted to engage each of the elements 12 and apply a force thereto which is suflicient to overcome the friction generated between the wall of the shells 14 and the supports 102 during expansion. This device is designed to generate, at its po-int of contact with the heat exchange elements 12, an amount of expansion which is approximately equal to the summation of the expansions undergone by the above-mentioned components. The device, called a force applicator 118, is best shown in FIG. ll and comprises an elongated cylindrical member which is provided with a plurality of projections or arms 122 extending from the surface thereof and adapted to engage all of the heat exchange elements 12 at their apices 20. The force applicator 118 is positioned within the vapor generator between two laterally spaced bundles of heat exchange elements, the former being maintained in position by means of the structural supports 124 and 126 and iixed at one end by means of lugs 128 and engaging members 130. This point of fixation is designated in FIG. 2 by the line'131. The arms 122 which are weldedly fixed to the surface of the cylindrical member 120 extend the full width of each of the heat exchange element rows so as to engage all of the elements 12. A pair of arms 122 are associated with each row of heat exchange elements 12 with each arm engaging the element on either side of the elements at their apex 20 such that they form force imparting members when the force applicator 113 is either expanding o'r contracting. The cylindrical member 120 is closed at both ends to form a chamber 132 which is iilled with a heat conducting material such as a liquid sodium or liquid sodium-potassium mixture. One of the ends of .member 120 is apertured, as at 134, to permit entry of a heating element 136 which extends Vsubstantially the full length of the chamber 132 and supplies the force applicator 118 with heating duid from the sodium main inlet circulator 74. The heating element 136 comprises a pair of concentrically arranged tubes 138 and 140 which are positioned in spaced relation to form a pair of passages 142 and 144 therethrough. The inner end of the inner tube 138 is spaced from the inner end of the outer tube 140 in order to establish communication between passages 142 and 144 and its other end extends beyond the outer end of tubes 140 to connect in fluid communication with the sodium main inlet circulator 74. A discharge line 146 is connected to the outer tube 140 to deliver the spent heating fluid to the sodium main outlet distributor 76. An expansion tank 148 is attached to the cylindrical member 120 in communication with the chamber 132 to accommodate expansion of the liquid sodiumpotassium mixture within the chamber.

The operation of t-he force applicator 118 is as follows. When the vapor generator 10 is in operation, liquid sodium is caused to ow through ltube 138 from the sodium main inlet distributor 74 to the force applicator heating element 136. Within the heating element 136 the liquid sodium makes two passes, one being in iiowing along passage 142 and the return pass being made in flowing along passage 144 to the discharge line 146. The hot liquid'sodium, which is at substantially the same temperature as that in the main inlet distributor 74, gives up a portion of its heat to the liquid sodium-potassium mixture in the chamber 132 which, in turn, heats the Wall of the cylindrical member 120 causing it to expand at the same rate as expansion occurs in the main inlet distributor 74. Expansion of the force applicator 118 causes a force to be imparted to the heat exchange elements 12 through the arms 122 in engagement therewith. The amount of expansion required is the sum of the expansion of the sodium main inlet distributor 74 from its point of yfixation 102 and the amount of expansion of the upper or hot leg 16 of the heat exchange elements 12. Or, in other Words, it is the distance through which the apex 20 on each of the heat exchange elements is caused to move by reason of the expansionundergone by the main inlet distributor and the upper leg 16 of the element.

It is therefore necwsary to form the force applicator 118 of a length such that the amount of expansion undergone by it'between its point of fixation 131 and the point at which its arms 122 engage the respective heat exchange elements 12 will be the same as'the sum of the expansion of the respective heat exchange elements plus the expansion of the main inlet distributor 74 between its xed point 102 and the header 32 to which the respective heat exchange elements connect. This length is calculated from the basic formula:

L=length of the force applicator 118 l1=horizontal length of a heat exchange element 12 l2=distance between the point of fixation 102 of the sodium main inlet distributor 74 and the header 32 which connects the outermost heat exchange element 12 Tl--the ave-rage metal temperature of the heat exchange elements 12 T2=metal temperature of the sodium main inlet distributor 74 T3= metal temperature of the force appliactor 118 T =ambient temperature a1=coeflicient of expansion of the heat exchange element material a2=coefficient of expansion of the sodium main inlet distributor material a3=coeicient of expansion of the force applicator material In order to bring about the results contemplated by the Iinstant invention it is contemplated to form the force applicator 118 of the same material or of a material having the same coefficient of expansion as the main inlet distributor 74 such that a2 in the above equation equals a3. However the heat exchange elements can be formed of a different material the only effect being to alter the length of the force applicator. In the preferred embodiment o-f the invention shown the metal temperature of the force applicator 118 is substantially the sarne as that of the main inlet distr-ibutor such that 'T2 equals T3.

Another consideration is the determination of the distance between the points of fixation of the force applicator 131 and the main inlet distributor 102. This distance is Lfound to be the difference between the horizontal length of a heat exchange element and the length of the force 4applicator that will yield the `same amount of expansion as does the heat exchange element.

Therefore, by anchoring a force applicator 118 such as that described :above at this point the `arms 122 thereon will impart a force on the lower ends of the hot legs 16 that will compel them to expand an amount as dictated by the expansion undergone by the main inlet distributor 74 and the heat exchange element itself thereby reducing the possibility of having one or more of the elements prevented lfrom so expanding because of an excessive amount of friction force develped by the relative sliding created between the surfaces of the shells 14 and the heat vexchange element .spacers 116. y

By forming fthe instant vapor generator arrangement of individual heat yexchange elements, the present design satisfies both modern and future power plant cycles without imposing restrictions to operating conditions or plant size. By ymerely Iadding to or subtractin-g from the number of heat exchange elements employed in the generator,`

the capacity of Ithe generator can be altered as desired. Moreover, the delivery of steam temperature capable of being developed in the instant generator is virtually unlimited being restricted Vonly by .the limitation imposed by the available materials.

In addi-tion, by forming the heat exchange elements of a V-shape wherein the hot leg is shorter in length than the cold leg there is provided a means to alleviate the strain developed in those connectors joining Athe heat exchange elements to the various headers. The difference in length between the two legs is such that when the hot leg lexpands during the operation of the generator its increase in length will be substantially .the same yas the increase in length realized in the cold leg. Therefore, the connectors 34 and 62 between the heat exchange elements and the sodium land water headers will not be overly stressed by the expansion and contraction experienced 'by the various pressure parts during generator operation.

The prevention of undue amounts of strain on the connectors 34 is further enhanced by the force applicator which is adapted to impart to the lower end of the hot lleg ofk each heat exchange element an expansion-inducing force that is adapted to overcome the expansion-resisting forces of friction which are generated when the elements expand through their spacing structure.l The force applicator, which is characterized by simplicity of form and operation, thus permits expansion of the generator 'components that is free of the danger of overstressing the connectors 34.

Furthermore, the unique `design of the heat exchange `elements minimizes the hazards associated with the accidental mixing of sodium and water; rst, by designing the ends lof the elements such -that should leaks develop in any of the welds serving to join the water be-aring tubes to the sodium bearing shell, where leaks are most apt to occur, the leaking elements, be it sodium or water, will fall into .the space between the end of the shell and the water manifold and. not into contact with the other element. Safety in the instant device is further enhanced by the fact that by forming .the generator from a large number of heat exchange elements only small volumes of s0- dium and water 4are handled by each of vtheelements there- 'by reducing the `amount of potential .danger due to leakage to la minimum.

The use of large numbers :of heat exchange elements each handling -small volumes of sodium also enhances the heat transfer stability of the generator by reducing the amount of heating uid stratification which would be present in generators employing large vol-ume shells for conducting the heating fluid. A

Maintenance and inspection of the generator is easily accomplished since all :of the heat exchange element connectors and operating fluid headers have liberal access and.

are readily available for inspection. In addition, Vall welds joining the elements to the headers have their entire periphery -accessible for repair. The remainder of the welds are accessible for visually inspect-ing a lgood portion of the weld periphery. Maintenance during operation, therefore, is the same, and perhaps even simpler than in convention-al power plant vapor generators.

It will be understood that various changes in the details, lmaterials, and arrangements of parts which have been herein described and illustrated in order to explain the nature of the invention, may be made 'by those skilled in the art within the principle and scope of the invention a expressed in the appended claims.

What is claimed is: 1. In a vapor generator apparatus adapted for the indirect transfer of heat from a heating fluid to a fluid to be heated, the combination of first longitudinally extending inlet and outlet distributors adapted to pass said heating fluid; second longitudinally extending inlet and outlet distributors adapted to pass said fluid to be heated; a plurality of nested, V-shaped, tubular heat exchange elements of equal length comprising substantially closed shell means and tube .means co-extensive with and enclosed by said shell means defining separate counterfiow passages for said fluids, said heat exchange elements being arranged in planes parallel -to the axis of said first inlet distributor and having one of said passa-ges connected between said first inlet and outlet distributors yand the other of said passages connected between said second inlet and outlet distributors whereby one leg of each of said heat exchange elements operates at a substantially greater temperature than lthe other; means engaging said heat exchange elements intermedia-te the ends thereof -for imparting thereto a `force capable of longitudinally extending said elements an amount equal to the combined longitudinal expansion of said first inlet distributor and said hot leg, said means comprising an elongated, thermally expandable tubular force applicator, engaging means connected to said force applicator to engage each of said heat exch-ange elements intermediate their ends and means for passing heating fluid through said force applicator.

2. In a vapor generator apparatus adapted for the indirect transter of heat from a heating fiuid to a fluid to be heated, the combination of first longitudinally extending, vertically spaced, parallel inlet and outlet distributors adapted to pass said heating fluid; second longitudinally extending, vertically spaced, parallel inlet and outlet distributors adapted to pass said fluid to be heated :arranged parallel to said first inlet and outlet distributor; a plurality of nested, V-shaped, tubular heat exchange elements of equal length comprising substantially closed shell 4means and -tube means co-extensive with and enclosed by said shell means defining separate counterow passages 4for said uids, said heat exchange elements being arranged in planes parallel to the ax of said distributors and each having one of said passages connected between said first inlet and outlet distributors and the other of said passages connected between said second inlet and outlet distributors whereby one leg of each of said heat exchange elements operates at a substantially greater temperature than the other; means engaging said heat exchange elements at' the apices thereof for impar-ting thereto a force capable of longitudinally extending said elements an amount equal to the combined longitudinal expansion of said first -inlet distributor and said hot leg, said means comprising an elongated, thermally expandable, Itubular force applicator arranged parallel to said distributors, engaging means connected to said force applicator to engage each of said heat exchange elements at their apices and means for passing heating iiuid through said force applicator.

3. The combination recited in claim 2 wherein said heat exchange elements comprise an elongated. V-shaped shell having closed ends defining one of said passages; apertures in said closed ends; a plurality of tubes extending Ithrough said shell substantially parallel to the axis thereof defining the Iother of said passages, said tubes extending throu-gh said apertures and having their ends spaced from the ends of said shell and manifold means spaced from said closed ends attaching said tubes for parallel ow.

4. The combination recited in claim 3 wherein the heat exchange element leg `conducting liuids at a higher temperature is formed shorter in length than the other leg by an amount proportional to the average 1metal ternperature of each leg.

5. In a vapor generator apparatus adapted for .the indirect transfer of heat from a heating fluid to a fluid to be heated, the combina-tion of first longitudinally extending, vertically spaced, parallel inlet and outlet distributors adapted to pass said heating uid; second longitudinally extending, vertically spaced, parallel inlet and outlet dis- Til tributors adapted to pass said tluid to be heated arranged parallel to said first inlet and outlet distributors with said second inlet distributor positioned adjacent said rst outlet circulator and said second outlet distributor positioned adjacent said rst inlet distributor; header means extending laterally from and being in communication with said distributors; a plurality of nested, V-shaped, tubular heat exchange elements of equal length comprising substantially closed shell means and tube means co-extensive with and enclosed by said shell means defining separate counterilow passages for said fluids extending between said distributors, said heat exchange elements being arranged in planes parallel to the axes of said distributors and each having one of said passages connected between header means associa-ted with said first inlet and loutlet distributors and the other of said passages connected between header means associated with said second inlet and outlet distributors whereby one leg of said of said exchange elements operates at a substantially greater temperature than the other; means engaging said heat exchange elements at the apices thereof for impar-ting thereto a force capable of longitudinally extending said elements an amount equal to the combined longitudinal expansion or" said vfirst inlet distributor and said hot leg, said means comprising an elongated, thermally expandable, tubular force applicator arranged parallel to said distributors land lying in a plane lcontaining said heat exchange element apices, engaging means connected lto said `force applicator to engage each of said heat exchange elements at their apices, and means for passing heating fluid through said force applica-tor.

6. The combination recited in claim 5 wherein s-aid heat exchange elements comprise an elongated, V-shaped shell having closed ends defining one of said passages; apertures in said closed ends; a plurality of tubes extending through said shell substantially parallel to the axis thereof defining the other of said passages, said tubes extending through said apertures and having their ends spaced from the ends ot said shell and mainfold means spaced from said closed ends attaching said `tubes for parallel flow.

7. The combination recited in claim 6 wherein the heat exchange element leg conducting fluids at a higher temperature is formed shorter in length than the other leg by an amount proportional to the average metal temperature ot' each leg.

8. In a vapor generator apparatus adapted for the indirect transfer of heat from a heating fluid to a uid to be heated, the combination of first longitudinally extending, vertically spaced, parallel inlet and outlet distributors adapted to pass said heating fluid; second longitudinally extending, vertically spaced, parallel inlet and outlet distributors to pass said fluid to be heated arranged parallel to said first inlet and outlet distributors with said second inlet distributor positioned adjacent said first outlet distributor and said second outlet distributor positioned adjacent said first inlet distributor, said first inlet distributor and second outlet distributor having vertically aligned points of zero axial expansion; hea-der means extending laterally from and being in communication with said distributors; a plurality of rows of nested, V-shaped, 4tubular heat exchange elements of equal length defining separate counterlow passages for said iluids extending between said distributors, said heat exch-ange elements being arranged in vertical planes parallel to the axes of said distributors;

- means connecting one of said passages between header means associated with said first inlet and outlet distributors and `means connecting the other of said passages between header means .associated with said second inlet and outlet distributors whereby one leg ot' each of said heat exchange elements operates at a substantially greater temperature than the other; -an elongated, thermally expandable, tubular force applicator in vertical alignment with said distributors and lying in a plane containing said heat exchange element apices, longitudinally spaced arms connected to said force `applicator to engage each row of said heat exchange elements at their apices, said force applicator having an axial length that will experience a longitudinal expansion that is equal to the combined expansion of said rst inlet circulator and the outermost row of heat exchange elements; means anchoring said force applicator at its inner end for zero expansion, and means connecting said force applicator to said rst inlet and outlet distributors. 'f- I 9. The combination recited in claim 8 wherein said heat exchange elements comprise an elongated, V-shaped 10 shell having closed ends dening one of said passages;

Vapertures -in said closed ends; a plurality of tubes extending through said `shell substantially parallel to the axis thereof dening the other `of said passages, said tubes extending .through said .apertures and having their ends spaced from the ends of said shell 'and manifold means spaced from said closed ends attaching said tubes for parallel ow. I

10. The combination recited in claim 9 wherein the heat exchange element leg conducting iluids at a higher temperature is formed shorter in length Ithan the other leg by an amount proportional to the 4average metal temperature of each leg.

References Cited by the Examiner UNITED STATES PATENTS.

2,413,360 12/1946 Maguire et al; 165-81 2,612,350 9/1952 Stadler 165-143 X 2,893,701 7/1959 Bell *1654-70 FOREIGN PATENTS 597,263 5/ 1960 Canada. 706,775 3/ 1931 France. 1,060,883 7/ 1959 Germany.

373,990 11/1930 Great Britain. 841,800 9/ 1958 Great Britain.

O CHARLES SUKALO, Examiners.

V. M. PERUZZI, Assistant Examiner. 

1. IN A VAPOR GENERATOR APPARATUS ADAPTED FOR THE INDIRECT TRANSFER OF HEAT FROM A HEATING FLUID TO A FLUID TO BE HEATED, THE COMBINATION OF FIRST LONGITUDINALLY EXTENDING INLET AND OUTLET DISTRIBUTORS ADAPTED TO PASS SAID HEATING FLUID; SECOND LONGITUDINALLY EXTENDING INLET AND OUTLET DISTRIBUTORS ADAPTED TO PASS SAID FLUID TO BE HEATED; A PLURALITY OF NESTED, V-SHAPED, TUBULAR HEAT EXCHANGE ELEMENTS OF EQUAL LENGHT COMPRISING SUBSTANTIALLY CLOSED SHELL MEANS AND TUBE MEANS CO-EXTENSIVE WITH AND ENCLOSED BY SAID SHELL MEANS DEFINING SEPARATE COUNTERFLOW PASSAGES FOR SAID FLUIDS, SAID HEAT EXCHANGE ELEMENTS BEING ARRANGED IN PLANES PARALLEL TO THE AXIS OF SAID FIRST INLET DISTRIBUTOR AND HAVING ONE OF SAID PASSAGES CONNECTED BETWEEN SAID FIRST INLET AND OUTLET DISTRIBUTORS AND THE OTHER OF SAID PASSAGES CONNECTED BETWEEN SAID SECOND INLET AND OUTLET DISTRIBUTORS WHEREBY ONE LEG OF EACH OF SAID HEAT EXCHANGE ELEMENTS OPERATES AT A SUBSTANTIALLY GREATER TEMPERATURE THAN THE OTHER; MEANS ENGAGING SAID HEAT EXCHANGE ELEMENTS INTERMEDIATE THE ENDS THEREOF FOR IMPARTING THERETO A FORCE CAPABLE OF LONGITUDINALLY EXTENDING SAID ELEMENTS AN AMOUNT EQUAL TO THE COMBINED LONGITUDINAL EXPANSION OF SAID FIRST INLET DISTRIBUTOR AND SAID HOT LEG, SAID MEANS COMPRISING AN ELONGATED, THERMALLY EXPANDABLE TUBULAR FORCE APPLICATOR, ENGAGING MEANS CONNECTED TO SAID FORCE APPLICATOR TO ENGAGE EACH OF SAID HEAT EXCHANGE ELEMENTS INTERMEDIATE THEIR ENDS AND MEANS FOR PASSING HEATING FLUID THROUGH SAID FORCE APPLICATOR. 